Cathode support structure



March 16, 1948. p, KUSCH 2,437,880

CATHODE SUPPORT STRUCTURE Filed July 9, 1945 I4- FIG. 'I 32 l5 0 30 3| IO I 1 27 29 I I 26 W l l flmla I II I! I I W V IL! I8 I 1 24 I I I I a I I 28 RADIAL TRAVEL OF CATHODE) as w CENTER LINE OF T DEGREE OF MAGNETRON STRUCTURE INVENTOR THE CATHODE POLYKARP KUSCH TRAVEL DUE TO BY THERMAL EXPANSION ATTORNEY Patented Mar. 16, 1948 2,437,880 CATHODE SUPPORT STRUCTURE Polykarp Kirsch, New York, N. Y., assignor to the erica as represented by the United States of Am Secretary of War Application July 9, 1945, Serial No. 604,073

4 Claims.

This invention relates in general to cathodes and more particularly to such cathodes which are applicable to magnetron tubes;

Some types of magnetrons comprise a cylindrical anode with a concentric indirectly heated cathode supportedby a lead-in wires. When the cathode is raised to its normal operating temperature, it is displaced radially by longitudinal thermal expansion of the lead-in wires. This is an undesirable result, because the asymmetrical condition will give a reduced efliciency for the magnetron.

It is therefore an object of this invention to provide a radially mounted cathode structure for an ultra-high-frequency magnetron, the cathode-supporting members being dimensioned to position the cathode coaxially with the anode when the magnetron is in operation thus compensating for the thermal expansion of the oathode-supporting members taking place with the beginning of the operating cycle of the magnetron.

This invention will best be understood by reference to the drawing in which Fig. 1 is a cross-sectional view of a magnetron taken along its axis and the axis of the cathode structure;

Fig. 2 is a plan View of the cathode and of the anode taken along line 2-2 illustrated in Fig. 3;

Fig. 3 is an enlarged partly sectional view of a portion of the anode and cathode of Fig. 1 illustrating the displacement of the cathode due to the thermal expansion of the cathode-supporting tungsten rods.

Referring now to drawings, they disclose a sectional view of the magnetron in Fig. 1 including only a portion of a wave guide output circuit l and a portion of the permanent magnets H and I2, these elements being not fully illustrated because the invention resides in the oathode structure. Permanent magnets H and I2 engage soft iron pole-pieces l3 and I 4, which are silver-soldered at !5 and IE to a copper shell I? thus completing the gas-tight connection between the shell and the pole-pieces. While the wave guide I0 is only partially illustrated in the figure, it is provided, in the portion which is not illustrated, with a gastight electrical window. This window seals-01f the inner chamber of the magnetron from atmospheric pressure. An anode I8 is held fixedly by shell ll, the axial length of the shell being suficiently long to provide two end spaces above and below the cathodeanode assembly. The cathode structure is of the radial type, tungsten rods 20 and 22 being used pair of radially extending.

for supporting the cathode cylinder 24 in central.

cathode assembly is supported by the tungstenrods ZOand 22 by means of molybdenum or nickel.

jumpers 27 and 2B, the latter being welded directly to the cathode hat and one end of the heater coil 25. The upper jumper 21, welded with its one end to rod 20, is fastened to an insulating washer 29 placed over the upper hat of the cathode. The upper end of the heater coil 26 passes through the center hole of the washer for making a weld joint with jumper 21, which completes the cathode and the heater circuit. The outer ends of the tungsten rods protrude beyond a glass seal 30, which is connected to a Kovar ring The Kovar ring is brazed to a copper ferrule 32, which is brazed to the copper shell ll of the magnetron. Thus it is the shell of the magnetron that actually supports the entire cathode assembly through the ferrule, the ring, the glass seal, and the tungsten rods. As illustrated in Fig. 2, the cathode structure is radially mounted with respect to the central cylindrical opening in the anode indicated by radius R; stated difierently, the center line, CL, of the entire cathode assembly passes through the axis of the magnetron.

The cathode is mounted so that its axis is parallel to the anode axis 36 and a slight amount ofi center in position 34 when magnetron is not in operation. When the cathode and the leads reach the operating temperature, there is a displacement of the cathode to position 36. If the original position 34 is chosen accurately, the operating position 36 will be such that the cathode will be positioned symmetrically with respect to the cylindrical anode and the cathode axis will be colinear with the anode axis. In one embodiment of the invention, the displacement of the cathode as it was heated was 0.005 inch.

While there has been described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. A thermionic tube, including a cylindrical putting the magnetron into displaced by a small anode structure, a cathode structure, and radially extending lead-in wires connected to said cathode, said wires, holding the axis of said cathode amount from the axis of said anode when the tube is de-energized, said wires being affected by current through the cathode and general heating of said tube causing the axis of said cathode and the axis of said anode to be substantially colinear after the tube has been energized and reached an operating thermal equilibrium.

2. A thermionic tube including an anode structure and a cathode structure, means, radial to the axis of said anode, holding the axis of said cathode displaced by a small amount from said axis of said anode when the magnetron is not operating, said means being afiected by current through the cathode and general heating of said tube causing the axis of the cathode and the axis of the anode to be substantially collnear when the cathode is energized.

3. A thermionic tube including a cylindrical anode, a cylindrical cathode, and two metallic rods supporting said cathode in radial relationship with respect to the axis of said anode, said rods holding said cathode in ofi-center position with respect to said axis when said tube is deenergized, and in center position after said tube reaches a thermal equilibrium typical of said tube during the operating state of said tube, whereby the thermal expansions of the tube structure, due to the temperature rise with the operation of said tube, establish the coaxial relationship between said anode and said cathode.

4. A thermionic tube including an anode, the locus of the inner surface of said anode being a. cylinder, a cylindrical cathode, and instrumentalities positioned in radial relationship with respect to the axis of said cylinder, completing the electrical circuits of and mechanically supporting said cathode, said instrumentalities expanding in the radial direction with the establishment of the operating temperature of said tube holding said cathode in coaxial relationship with said cylinder.

- POLYKARP KUSCH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,103,362 Hansell Dec. 28, 1937 2,130,510 Samuel Sept. 20, 1938 2,154,758 Dallenbach Apr. 18, 1939 2,232,550 Rice Feb. 18, 1941 

